Dynamic keying circuit for musical instrument



Sept. 1, 1970 VAR/ABLE VOLT/16E ATTACK A. B. FREEMAN DYNAMIC KEYING CIRCUIT FOR MUSICAL INSTRUMENT Filed April 16, 1968 VAR/ABLE Hg 5 V/IBMBLE BIAS TONE CENEEATOQ C/ECU/ 7" I N VENTOR.

BY r-w-w ATTORNEYS United States Patent 3,526,702 DYNAMIC KEYING CIRCUIT FOR MUSICAL KNSTRUMENT Alfred B. Freeman, Skokie, lll., assignor to Chicago Musical Instrument Co., Lincolnwood, 111., a corporation of Delaware Filed Apr. 16, 1968, Ser. No. 721,813 Int. Cl. (31% 1/02, 1/00 U.S. Cl. 84-1.26 17 Claims ABSTRACT OF THE DISCLOSURE A keying circuit is provided for an organ to control coupling of a tone signal source to an output circuit, and includes key-actuated switching means and an RC timing means to produce a controlling voltage inversely proportional to the time required for a movable contact of the key actuated switching means to move from one contact to another, and thus proportional to the force with which the playing is struck.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to a dynamic electrical keying circuit which allows the audio output of an organ to be similar to the audio output of a piano by controlling the attack and/or decay.

Description of the prior art In an electronic organ the volume level in ordinary playing is established by the position of the expression pedal. The expression pedal allows the volume level to be adjusted by the players foot from soft to a maximum pre-set level. When a piano is played, the force with which the pianist strikes the piano keys determines the amplitude of the sound, but in organs of the prior art the force with which the organ keys are struck does not affect the output signal level of the organ. Moreover in pianos, the sound eventually terminates even though the key is held down, while in organs, the output continues as long as the key is depressed.

SUMMARY OF THE INVENTION A keying circuit for an electronic organ having manual keys for keying tone generators to audio output circuits in which the force with which tre keys are struck by the player determines the audio output level. A first charging circuit is normally grounded and when a key is depressed it actuates a switch and a bias means starts to charge it. A second charging circuit is normally charged and is connected by the switch to the first charging cirouit. The time for tre movable contact of the switch to move from a first to a second position determines the level to which the bias source charges the first charging circuit before the movable contact reaches the second position. The second charging circuit completes charging of the first charging circuit after the movable contact reaches the second position. The potential across the second charging circuit controls the audio output level and thus the time required for the movable contact of the switch to move from a first to a second position determines the audio output level. A second switch has a movable contact also controlled by a key which in a first position establishes the potential level on the second charging circuit and in a second position provides a key hold-on function.

Other objects, features and advantages of the present invention will be readily apparent from the following de- 3,526,192 Patented Sept. 1, 1970 tailed description of a certain preferred embodiment thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic diagram of the dynamic keying circuit of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The figure illustrates a capacitor C which has one side connected to ground and the other side connected to a resistor R The other side of the resistor R is connected to a resistor R which has its other side connected to the output of an attack variable voltage 10. The attack variable voltage 10 receives an input from B plus terminal 11. The attack variable voltage 10 may be a source of voltage which varies in amplitude. A switch S has its movable contact 11 connected to the junction point between resistors R and R and in a first position engages a terminal 12 which is connected to ground. In a second position, the movable contact 11 engages a contact 13 which is connected to the cathode of a diode D The other side of the diode D is connected to a base of a transistor T For illustrative purposes the transistor T is shown as a pnp type, but it is to be realized that an npn type transistor may be used by merely changing the bias voltages.

Contact 13 is also connected to a resistor R; which has its other side connected to B plus terminal 14. The emitter of the transistor T is also connected to terminal 14. A capacitor C has one side connected to the collector of the transistor T and its other side connected to the base of the transistor T A resistor R is connected from the base of transistor T to a resistor R The other side of resistor R is connected to a suitable variable bias source 16 which might be controlled, for example, by control knob 17.

A switch S has a first stationary contact 18 which is connected to the junction point between resistors R and R A movable contact 20 of switch S is connected to a variable bias source 19 which may be controlled by the knob 21.

A second stationary contact 22 of switch S is connected to a resistor R which has its opposite side connected to a modulating or gating circuit 23. The gating circuit 23 is also connected to the collector of the transistor T and to capacitor C For each playing key, there is a tone generator 24 which supplies an input to the gating circuit 23. An output circuit 26 receives the output of the various gating circuits 23.

The movable contacts 11 and 20 of switches S and S are linked together :by a mechanic linkage 25 so that they move in synchronisrn.

A key 27 of the organ is coupled to the linkage 25 so as to move switch contacts 11 and 20. The key 27 is one of the keys of the organ and it is to be realized that there will be a dynamic keying circuit according to this invention controlled by each of the keys of the organ, if desired. For illustrative purposes only, an individual key 27 is shown.

In operation, the force with which the key 27 is hit by the player of the organ determines the time for switch contacts 11 and 20 of switches S and S to move, respectively, from contacts 12. to 13, and 18 to 22. Thus, if the key 27 is hit very hard by the player, the switch contacts 11 and 20 will take a relatively short time to move from the contacts 12 and 18 to the contacts 13 and 22, respectively. On the other hand, if the key 27 is hit relatively hard by the player the switch contacts 11 and 20 will move from the contacts 12 and 18, to the contacts 13 and 22, respectively, very rapidly. The dynamic keying circuit of this invention produces a larger amplitude output when the key 27 is hit hard than when the key 27 is hit lightly. The invention produces a relatively low amplitude output when the key 27 is hit lightly by the player and the switches 11 and 20 move slowly between contacts 12 and 18 to contacts 13 and 22, respectively The B plus voltage connected to terminals 9 and 14 might be plus twenty volts, for example. The variable bias sources 16 and 19 might be adjustable between 19 and 40 volts, for example.

When the switch contacts 11 and 20 are in engagement with the contacts 12 and 18 respectively, which occurs before the key 27 is depressed by the player, the charge on the capacitor C will be zero. This is because the switch contact 11 is connected to ground through terminal 12 and the capacitor will discharge through resistor R to ground if it initially had any charge. The capacitor C will be charged to the potential of the variable bias 19 because contact 20 engages terminal 18.

When the key 27 is depressed, the contacts 11 and 20 will move out of engagement with terminals 12 and 18, respectively, and there will be a time delay before these contacts engage contacts 13 and 22, respectively. During this time, the capacitor C will be at least partially charged from the attack variable voltage 10. When contact v11 engages contact 13, the capacitor C will supply current through the diode D and resistor R to complete the charge on capacitor C to the voltage level of the capacitor C The time that current will be drawn from capacitor C to charge capacitor C will depend upon the time that it takes the contact 11 to move from the reference bias contact 12 to contact 13. If this time is relatively short, the capacitor C will be only slightly charged when contact 11 engages contact 13 and it will take a relatively larger amount of charge from capacitor C to completely charge the capacitor C On the other hand, if the contact 11 takes a relatively long time to move from contact 12 to contact 13, the capacitor C will be substantially charged when the contact 11 engages the contact 13 and it will take a relatively small amount of charge from the capacitor C to complete charging of the capacitor C The result is that the charge transferred between capacitors C and C varies as a function of the time delay of switch S As the capacitor C discharges into the capacitor C the potential at the base of the transistor T remains substantially constant while the voltage on the collector of the transistor goes up proportionally by the amount of charge transferred to the capacitor C When the collector voltage reaches about one-half volt or more, the gating circuit 23 allows the signal from the tone generator 24 to be supplied to the output circuit 26. The gating circuit has an output which varies with the potential on the collector of the transistor T and the voltage on the collector of transistor T controls the gain of the gating circuit 23. Thus, if the key 27 is hit hard the gating circuit 23 has a high output and the output from the output circuit 26 will be a high energy signal. n the other hand, if the key 27 is hit lightly, the gating circuit 23 will have a lower output and the output from the output circuit 26 will be relatively small.

When switch contacts 20 of switch S engages contact 22, resistor R provides a key hold-on function with the variable bias 19 supplying the holding signal.

The bias source 19 charges the capacitor C through contact 18 in the key-up position. On key-down position, the capacitor C transfers charge through the contact 13 to the capacitor C as explained above. Such transfer is augmented by a very small amount by the bias source 16 through the high resistances R and R until the diode D cuts off,- whereupon the capacitor C is slowly recharged through the key-down decay resistor R to provide a key-down decay rate. The bias source 16 is variable to enable selection of said decay rate, and if the decay rate is set sufiiciently high, a sustain will be produced. On release of the key, bias source 19 continues the decay at a rate determined by its setting to provide a key-up decay rate.

Resistor R assures that diode D is cut off when a low attack voltage is used, and thus enables the circuit to be operated in low dynamic keying ranges.

The terms discharging and charging as used herein are used to designate a direction relative to each other, and are each to be treated as having a reversed meaning when equivalent reversals are made in the circuit.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. A dynamic keying circuit for an electronic organ having manual keys for keying tone generators to audio output circuits comprising,

(a) a first capacitor;

(b) a first resistor connected to the first capacitor;

(c) a first switch with a movable contact controlled by one of the manual keys, the movable contact of the first switch connected in circuit with the first capictor and the first resistor and movable to a first position to discharge the first capacitor;

(d) a first bias means connected in circuit with the first resistor and first capacitor to charge the capacitor when the movable contact of the first switch is moving from the first position to a second position;

(e) a second capacitor connected to the first switch and to the first resistor and the first capacitor when the first switch is in the second position;

(f) a second bias means connected to the second capacitor to charge it;

(g) a second resistor in circuit with the second bias means and the second capacitor; and

(h) a gating means in circuit between one of the tone generators and one of the audio output circuits, and connected to the second capacitor.

2. A dynamic keying circuit as claimed in claim 1 comprising a second switch with a movable contact controlled by the same manual key which controls the movable contact of the first switch, and further bias means connected to the movable contact of the second switch to connect the further bias means in circuit with the second resistor and the second capacitor when the second switch is in a first position.

3. A dynamic keying circuit according to claim 1 comprising an attack variable voltage source connected in circuit with the first bias means and the movable contact of the first switch.

4. A dynamic keying circuit according to claim 3 comprising a resistor connected in circuit between the attack variable voltage source and the movable contact of the first switch.

5. A dynamic keying circuit according to claim 1 comprising a key-down decay resistor connected in circuit between the second bias means and the second resistor.

6. A dynamic keying circuit according to claim 1 comprising a resistor connected in circuit between the first switch when in its second position and a bias means.

7. A dynamic keying circuit for an electronic organ having manual keys for keying tone generators to audio output circuits comprising:

(a) a first capacitor;

(b) a first resistor connected to the first capacitor;

(c) a first switch with a movable contact controlled by one of the manual keys, the movable contact of the first switch connected in circuit with the first capacitor and the first resistor and movable to a first position to discharge the first capacitor;

((1) a first bias means connected in circuit with the first resistor and first capacitor to charge the capacitor when the movable contact of the first switch is moving from the first position to a second position;

(e) a second capacitor connected to the first switch and to the first resistor and the first capacitor when the first switch is in the second position;

(f) a second bias means connected to the second capacitor to charge it;

(g) a second resistor in circuit with the second bias means and the second capacitor;

(h) a gating means in circuit between one of the tone generators and one of the audio output circuits, and connected to the second capacitor;

(i) a control amplifier with a first control electrode connected to one side of the second capacitor and a second control electrode connected to the other side of the second capacitor; and

(j) a third bias means connected to a third electrode of the control amplifier.

8. A dynamic keying circuit according to claim 7 wherein the control amplifier is a transistor.

9. A dynamic keying circuit for an electronic organ having manually operated keys for keying tone generators to an audio output circuit comprising,

(a) a first electronic timing means,

(b) first biasing means connected to the first electronic timing means,

(c) a second electronic timing means,

(d) a second biasing means connected to the second electronic timing means,

(e) a reference bias,

(f) a first switching means responsive to one of said keys and connecting said reference bias to a point between said first electronic timing means and said first biasing means when in a first position, and connecting said point to said second electronic timing means when in a second position, and

(g) a gating means connected in circuit between one of the tone generators and the audio output circuit and connected to the second electronic timing means.

10. A dynamic keying circuit according to claim 9 comprising,

(a) a second switching means; and

(b) a further biasing means connected to the second switching means and connected by the second switching means to the second electronic timing means when the second switching means is in a first position.

11. A dynamic keying circuit according to claim 9 comprising an attack variable voltage means connected in circuit with the first biasing means and the first switching means.

12. A dynamic keying circuit according to claim 9 com prising key-down decay means connected in circuit between the second biasing means and the second electronic timing means.

13. A dynamic keying circuit for an electronic organ having manual keys for keying tone generators to audio output circuits comprising:

(a) a first capacitor;

(b) a first resistor connected to the first capacitor;

(0) a first switch with a movable contact controlled by one of the manual keys, the movable contact of the first switch connected in circuit with the first capacitor and the first resistor and movable to a first position to discharge the first capacitor;

(d) a first bias means connected in circuit with the first resistor and first capacitor to charge the capacitor when the movable contact of the first switch is moving from the first position to a second position;

(e) a second capacitor connected to the first switch and to the first resistor and the first capacitor when the first switch is in the second position;

(f) a second bias means connected to the second capacitor to charge it;

(g) a second resistor in circuit with the second bias means and the second capacitor;

(h) a gating means in circuit between one of the tone generators and one of the audio output circuits, and connected to the second capacitor; and

(i) a diode connected between the second capacitor and the first switch and connected to the first resistor and first capacitor when the first switch is in the second position.

14. A dynamic keying circuit for an electronic organ having manual keys for keying tone generators to audio output circuits comprising:

(a) a first capacitor;

(b) a first resistor connected to the first capacitor;

(c) a first switch with a movable contact controlled by one of the manual keys, the movable contact of the first switch connected in circuit with the first capacitor and the first resistor and movable to a first position to discharge the first capacitor;

(d) a first bias means connected in circuit with the first resistor and first capacitor to charge the capacitor when the movable contact of the first switch is moving from the first position to a second position;

(e) a second capacitor connected to the first switch and to the first resistor and the first capacitor when the first switch is in the second position;

(f) a second bias means connected to the second capacitor to charge it;

(g) a second resistor in circuit with the second bias means and the second capacitor;

(h) a gating means in circuit between one of the tone generators and one of the audio output circuits, and connected to the second capacitor;

(i) a second switch with a movable contact controlled by the same manual key which controls the movable contact of the first switch;

(j) further bias means connected to the movable con tact of the second switch to connect the further bias means in circuit with the second resistor and the second capacitor when the second switch is in a first position; and

(k) a key hold-on resistor connected to the gating means and the second switch and connected to the further bias means when the movable contact of the second switch is in a second position.

15. A dynamic keying circuit for an electronic organ having manually operated keys for keying tone generators to an audio output circuit comprising:

(a) a first electronic timing means;

(b) first biasing means connected to the first electronic timing means;

(c) a second electronic timing means;

(d) a second biasing means connected to the second electronic timing means;

(e) a reference bias;

(f) a first switching means responsive to one of said keys and connecting said reference bias to a point between said first electronic timing means and said first biasing means when in a first position, and connecting said point to said second electronic timing means when in a second position;

(g) a gating means connected in circuit between one of the tone generators and the audio output circuit and connected to the second electronic timing means;

(h) control amplifying means with a first control electrode connected to one side of the second electronic timing means and a second control electrode connected to another side of the second electronic timing means; and

(i) a third biasing means connected to a third electrode of the control amplifying means.

16. A dynamic keying circuit for an electronic organ having manually operated keys for keying tone generators to an audio output circuit comprising:

(a) a first electronic timing means;

(b) first biasing means connected to the first electronic timing means;

(c) a second electronic timing means;

(d) a second biasing means connected to the second electronic timing means;

(e) a reference bias;

(f) a first switching means responsive to one of said keys and connecting said reference bias to a point between said first electronic timing means and said first biasing means when in a first position, and connecting said point to said second electronic timing means when in a second position;

(g) a gating means connected in circuit between one of the tone generators and the audio output circuit and connected to the second electronic timing means; and

(h) a unilateral current means connected in circuit between the first and second electronic timing means when the switching means is in the second position.

17. A dynamic keying circuit for an electronic organ having manually operated keys for keying tone generators to an audio output circuit comprising:

(a) a first electronic timing means;

(b) first biasing means connected to the first electronic timing means;

(c) a second electronic timing means;

(d) a second biasing means connected to the second electronic timing means;

(e) a reference bias;

(f) a first switching means responsive to one of said keys and connecting said reference bias to a point between said first electronic timing means and said first biasing means when in a first position, and connecting said point to said second electronic timing means when in a second position;

(g) a gating means connected in circuit between one of the tone generators and the audio output circuit and connected to the second electronic timing means;

(h) a second switching means;

(i) a further biasing means connected to the second switching means and connected by the second switching means to the second electronic timing means when the second switching means is in a first position; and

(j) a key hold-on means connected to the gating means and the second switching means, and connected to the further biasing means when the second switching means is in a second position.

References Cited UNITED STATES PATENTS 2,126,464 8/1938 Hammond 84l.26 X 2,482,548 9/1949 Kerkhof 84l.26 3,248,470 4/1966 Markowitz et a1. 84l.26 X 3,333,042 7/1967 Brombaugh 84l.26 X

ELI LIEBERMAN, Primary Examiner 25 S. CHATMON, 1a., Asistant Examiner US. Cl. X.R. 

